The antimicrobial uses of ozone and ionizing radiation, particularly ultraviolet ("UV") radiation, are well known for purifying water. Both agents are widely used to sterilize or purify water that is to be used for human consumption, and to purify effluent discharged from industrial processes. Other uses include the purification of recirculating water used in swimming pools and hot tubs, as well as the effluent of portable facilities, such as are found on boats. Due to the reactive nature of ozone, and to the volumes required for such uses, it is important that ozone be generated at or near the reaction chamber wherein the ozone is combined with the contaminated water. Accordingly, it is desirable to provide an efficient means for generating relatively large volumes of ozone with a relatively simple, inexpensive and compact apparatus.
It is understood that although reference is generally made herein to water as the contaminated medium, such devices may as well be used to treat other contaminated fluids.
Both single mode (i.e., employing UV or ozone alone as the sterilizing agent) and dual mode sterilizers have been in use for many years. Typically, a single mode device employs a UV tube to expose contaminated water to ionizing radiation, or exposes an air stream to UV radiation to generate ozone from the oxygen in the air, with the ozonated air then being mixed with the contaminated water. An old example of an ozone-producing apparatus is disclosed in U.S. Pat. No. 1,505,669 (Quain), wherein a UV lamp is positioned within an outer cylinder, with means for passing air between the tube and cylinder. The ionizing radiation emitted by the U.V. lamp reacts with the oxygen within the air passing by the tube, and ozonates the oxygen. The basic elements outlined in Quain are found, with various refinements, in virtually all ozone generators and dual mode sterilizers. See, for example U.S. Pat. Nos. 4,141,830 (Last); 4,179,616 (Coviello et al.); 4,189,363; and 4,230,571 (Dadd).
At its simplest, a dual mode sterilizer comprises: a) a UV lamp or other source of ionizing radiation enclosed within a chamber, within which a stream of oxygen-containing medium, usually air, is exposed to the radiation generated by the lamp; and b) a second chamber isolated from the first chamber, within which a stream of contaminated water flows and is therein exposed to radiation from the UV lamp. There may be provided means, either external to the device or incorporated therein, for combining the contaminated water with the ozonated air generated by the device.
In order to achieve maximum efficiencies in generating ozonated air, it is important that the air flowing past the ionizing element be relatively cool and dry. Various means have been employed to reduce the humidity in the air flowing through the device, including the provision of a desiccant-containing dryer (U.S. Pat. No. 4,230,571). This approach requires either regular replacement of the desiccant, or a means for continuously drying the desiccant to maintain effective functioning of the apparatus. It is desirable to provide a means for drying the air that doesn't require an external "active" air drying means or a desiccant. Preferably, the drying means requires little further energy consumption beyond that used in the other components of the apparatus, is relatively simple, and doesn't heat the air excessively.
A further drawback of present devices is that the UV lamp remains on at full force at all times during operation of the device, regardless of the flow of contaminated water through the device. This results in unnecessary heat buildup, shortened lamp life and increased power consumption in applications where flow rate varies. It is desirable to provide a means for reducing the lamp intensity as the flow rate through the device diminishes.